Dowel rod anchor



S p 1953 s. J. CROCKETT $650,476

DOWEL ROD ANCHOR Filed July 11, 1952 all\ Jami m "III/IIIIIIIIIA INVENTOR ATTORNEYS Patented gept. l, 1953 UNITED STATES PATENT OFFICE DOWEL non ANCHOR Samuel J. Crockett, Philippi, W. Va.

Application July 11, 1952, Serial No. 298,390

20 Claims.

My invention relates to improvements in means for safely supporting the roof of an underground mine or other tunnel; and in particular relates to an improved means for anchoring the inner ends of dowel rods within bores drilled in the roof of the mine, which bores may be drilled by any conventional method.

The recent trend in securing the roofs of certain types of mines against cave-ins ha been to drill bores diagonally upwardly into the strata above the roof of the mine, and to drive a snuglyfitting dowel rod into the bore, the rod havin an automatic anchoring means at its inner end, which means is actuated when the dowel arrives at the blind end of the bore. The dowel rod furnishes a certain degree of vertical support to the rock strata above the roof but is primarily intended to prevent lateral shifting of the strata resulting from vibrations set up in the mine while it is being Worked. Such lateral shifting breaks the natural bond between the various superjacent strata in the mine roof, and causes cave-ins. By driving the dowel rods into the afore-mentioned bores, the rock strata are pinned together to prevent such lateral shifting.

Until recently, the practice of the industry has been to use metal pins within the bores, such pins being, however, relatively expensive to purchase and being waseful of valuable metal since these pins usually cannot be removed from the bores when the mine tunnel is to be abandoned. Therefore, the present trend has been toward the use of wooden dowel rods, and the present invention is intended to provide an inexpensive and efiicient anchor for the inner ends of said rods.

The primary object of my invention is to provide an efficient and reliable anchoring means providing a double-acting wedge action, said anchor consisting of a center wedge adapted to force a plurality of adjacent slip members outwardly to engage the sides of the bore, the slip members being located in slots having reversed or upwardly narrowing tapers which cause the slips to forcibly spread the upper end of the dowel rod to further tighten the engagement thereof with the bore.

Another important object of my invention is to provide a trip means associated with the center wedge of the anchor, which trip means is actuated by abutting the blind end of the bore to drive the wedge downwardly and cause lateral spreading of the slips and engagement thereof with the walls of the bore.

Still another object of my invention is to provide the bore-engaging surfaces of the slip members with transverse striations to assist in gripping the walls of the bore and also to undercut the lower ends of said members so as to leave downwardly projecting teeth at the bottom ends thereof, said teeth tendin to dig into the bore walls and prevent further downward motion of the slips when the dowel is partially retracted outwardly with respect to the bore.

Another very important object of my invention is to provide an anchor means of the character specified which eliminates the necessity of hammering the dowel violently from below to cause setting of the anchor, such hammering tending to cause injury to the rod, as well as having a tendency to loosen the strata in the mine roof, and thereby contribute to a subsequent cave-in.

The present dowel rod may be provided with a bearing plate at its lower end which is screwed to said lower end after the dowel rod is in place in the bore, the tightening of said screw means causing retraction of the dowel rod for a distance suflicient to drive the slip members tightly into the reversed taper, thereby spreading the inner end of the dowel rod into tight engagement with the inner walls of the bore.

Other objects and advantages of my invention will become apparent during the following discussion of the drawings, wherein:

Figure 1 is a section through the roof of a mine, showing one of my dowel rods secured in place.

Fig. 2 is a section view taken along line 2-2, Fig. 1, and somewhat enlarged.

Fig. 3 is a section view taken along line 3-3, Fig. 1, and somewhat enlarged.

Fig. 4 is a perspective view showing the inner wedge and associated trip means and showing the two outer slip members there adjacent.

Referring to the drawings, above the roof R of the mine are rock strata S frequently comprising relatively large slabs. As shown in Fig. 1, the lowermost stratum is sometimes draw slate D which has a tendency to crumble and fall. A bore H is drilled upwardly into the strata S and receives the dowel rod I, the latter having, in the illustrated embodiment, a bifurcated inner end dividing the end into portions Ia and lb. The outer end of the dowel is provided with an axial bore lc for the purpose hereinafter set forth.

As shown in Fig. 1, the bifurcated upper portions la and lb define a slot having an upper narrow portion Id and tapering downwardly and outwardly along a portion Ie, to form the afore- 3 mentioned reversed wedge, the tapered portion le normally housing two slip members 2 separated by a Wedge 3. The lower ends of the tapered portion of the slot is are provided with footings if so that before the anchor is expanded and set, the lower ends 2a of the slip members 2 rest against the footings If, the slips 2 fitting snugly Within the tapered walls le of the slot, and the bore-engaging edges 2b of the slips being flush with the outer peripheryof the-dowel rod I.

As shown inFigs. 2 and 4, the inner surfaces 20 of the slip members .2 are upwardly and outwardly tapered at an angle which is complementary to the tapered surfaces 3a of the wedge 3. When the anchor is in its initial or unset position, the lower end 3b of the wedge 3 is even-with'th'elower ends 211 of the members 2, andthe tripbar 4 extends upwardly beyond the upper end of the dowel rod 5. But as the dowel rod is driven upwardly into the bore H, the upper end of the trip 4 abuts against theblind end of the bore H so that upon further insertion of the dowel rod into the bore H, the wedge 3 is pressed downwardly with respect to the-members 2 by the trip 4 and the surfaces 3a of the wedge 3 press against the complementary surfaces 20 of the slip members 2 and cause'said members to spread laterally outwardly with respect to the outer periphery of the dowel rod I and engage the walls of the bore H.

The outer lower ends of the slips 2 are undercut as at 2:1 so as to provide toothlike portions 2e which dig into the walls of the bore H and prevent downwardmotion on'the part of the members '2 with respect to said walls. The outer boreengaging surfaces 2b of the members 2 are further provided with a plurality of striations .21 to secure a better-grip on the walls of the bore I-I.

Note in Fig. 2 that the dowel rod l is also provided with an additional slot lg extending downwardly from the tapered slot le and adapted to provide clearance for the lower'end of the-wedge 3 when thelatter ispressed downwardly to expand the slips 2 as the anchor is set in the bore.

Atthe lower end'of the dowel rod l is a bearing plate 5 having a hole 5a therethrough, Fig. l. A screw 6 extends upwardly through the hole 5a and into the bore 10, the bore lc having been drilled to the root diameter of the threads on the screw 6 so as to provide a-strong grip when the screw is tightened therein.

In addition, a collar 7 is provided around the lower end of the dowel I so as to counteract any tendency that the screw may have to split the lower end of the dowel. This bearing plate 5 may be any desired shapeandis provided for the purpose hereinafter described.

The device is used as follows:

The bore H is first drilled upwardly into the rock strataS and is slightly longer than the length of the dowel rod I. The slips 2 are placed snugly within-the slot-portion is so that they'will not fall out, and-the wedge 3 is placed between the slips 2 with the bottom end 31) of the wedge approximately even with the bottoms Zwof the slips 2, so that in this position the outer surfaces 2bof theslips '2 are flush with theouter periphery of thedowel rod I, the trip 4 extending upwardly well above the inner end of the dowel rod 1. When the-dowel rod is'inserted in the bore II, the trip 4 abuts the blind end of the bore H, andthe outer end of .the dowel rod l is tapped upwardly from below-so as to drive the trip land the .wedge 3-downwardly with respect to the slips 2, thereby spreading the latter outwardly and digging them tightly into the walls of the bore The bearing plate 5 is then placed against the roof of the mine, and the screw 6 is passed through the hole 5a and is screwed tightly into the bore lc, thereby causing a slight retraction of the dowel rod within the bore I-I. Since the slips 2 have dug into the walls of the bore H and the teeth 26 are tightly secured therein to prevent shifting of the slips longitudinally of the bore I-I, upon the slight retraction of the dowel rod I caused "bythe tightening-of'the screw 6 the tapered walls le of the slot will move downwardly with respect to the slips 2 so that the bifurcated ends Ia, lb of the dowel rod will be forced to spread outwardly, thereby providing additional anchoring of the inner end of the dowel rod l, the retraction of the dowel rod l with respect to the bore being only over a relatively short distanceX, Fig. 2. The plate 5 also serves to provide some vertical support for the draw slate layer D.

As stated in the objects of this invention, the above assembly, because of the reversed wedge,

provides an anchoring action which is augmented by any downward movement of the dowel rod .1 'with'respect-to the slips .2 so that the :greater the downward pull on the dowel rod, the tighter the anchor is set within the upper end of the bore H.

I do not limit my invention to the exact form shown in the drawings, for obviously changes may be made therein within the scope of the claims. 7

I claim:

1. A strata dowel to be anchored in a blindend bore in the roof of a mine for securing together the strata thereabove, comprising a rod substantially the diameter of said bore, said rod being bifurcated at its upper end by a slot extending axially thereinto, the slot being tapered to converge upwardly; a pairof complementarily tapered slips in said'slot, the slips being spaced apart and-having inner adjacent surfaces tapering to diverge upwardly; a wedge between said slips having a taper complementary to that .of said inner adjacent surfaces; and van'elongated trip bar fixed to the top of'said wedge and extending upwardly out of said slot and beyond the end of said rod, whereby as said rodtis pushed into-said bore the trip bar will bottom on .said blind end and force said wedge downwardly with respect to saidslips thereby expanding the slips laterallyoutwardly to embed them in the-walls of the bore sothata downward pull on said rod will cause said slips to wedge deeper into'the taper of said slot and expand said bifurcated upper end.

2. In a device as set forth in claim 1, said slips each having an outer bore-engaging'surface'having striations thereon to tightly grip the Walls of said-bore, andthe lower end of saidslips each being undercut to leave tooth-like projections'to prevent shifting of s-aidrslips'axially of said bore.

3. In a device as set forth in claiml, said bore being deeper than the length of said rod, and said rodhaving a second bore inits lower-end; a bearing plate having a hole therethroughgand'a screw adapted to transfix 'said-hole and said sec- 0nd bore, whereby iwhen' said rod is inserted in said first bore with its lower end'above the roof of the mine and said screw is tightenedgthe rod will be forcibly moved downwardiyin said first bore to wedge'said slips.

4. A strata dowel to be anchored in a blindend bore in the roof of a mine for securing togather the strata thereabove, comprising a rod substantially the diameter of said bore, saidrod being bifurcated at its upper end by a slot extending axially thereinto, the slot being tapered to converge upwardly; a pair of complementarily tapered slips insaid slot, the slips being spaced apart and having inner adjacent surfaces tapering to diverge upwardly; a wedge between said slips having a taper complemetary to that of said inner adjacent surfaces and said Wedge extending upwardly out ofsaid slot and beyond the end of said rod, whereby as said rod is pushed into said-bore the wedge will bottom on said blind end and be forced downwardly with'respect to said slips thereby expanding the slips laterally outwardly to embed them in the walls of the bore so that a downward pull on said rod will cause said slips to wedge deeper into the taper of said slot and expand said bifurcated upper end. I l i In a device as set forth in claim 4, said slips each having an outer bore-engaging surface having striations thereon to tightly grip the walls of said bore, and the lower end of said slips each being undercut to leave tooth-like projections to prevent shifting of said slips axially of said bore.

6. In a device as set forth in claim 4, said bore being deeper than the length of said rod, and said rod having a second bore in its lower end; a bearing plate having a hole therethrough, and a-screw adapted to transfix said holeand said second bore, whereby when said rod is inserted in said first bore with its lower end above the roof of the mine and said screw is tightened, the rod will be forcibly moved downwardly in said first bore to wedge said slips.

'7. A strata dowel to be anchored in a blindend bore in the roof of a mine for securing together the-strata thereabove, comprising a rod substantially the diameter of said bore, said rod having at its upper end a' slot extending axially thereinto, the slot being tapered to converge upwardly; a pair of complementarily tapered slips in said slot, the slips being spaced apart and having inner adjacent surfaces tapering to diverge upwardly; a wedge between said slips having a taper complementary to that of said inner adjacent surface and said wedge extending upwardly out of said slot and beyond the end of said rod, whereby as said rod is pushed into said bore the wedge will bottom on said blind end and be forced downwardly with respect to said slips thereby expanding the slips laterally outwardly to embed them in the walls of the bore so that a downward pull on said rod will cause said slips to wedge deeper into the taper of said slot and expand the upper end of the rod.

8. In a device as set forth in claim 7, said slips each having an outer bore-engaging surface having striations thereon to tightly grip the walls of said bore, and the lower end of said slips each being undercut to leave tooth-like projections to prevent shifting of said slips axially of said bore.

9. In a device as set forth in claim '7, said bore being deeper than the length of said rod, and said rod having a second bore in its lower end; a bearing plate having a hole therethrough, and a screw adapted to transfix said hole and said second bore, whereby when said rod is inserted in said first bore with its lower end above the roof of the mine and said screw is tightened, the rod will be forcibly moved downwardly in said first bore to wedge said slips.

10. A strata dowel to be anchored in a blindend bore in the roof of. a mine for securing to gether the strata thereabove, comprising a rod substantially the diameter of said bore, said rod having a concentric bore in itsupper end and slots through its upper end communicating with said second bore, each slot being tapered to con verge upwardly; a complementarily tapered slip in each slot, the slips being spaced from the axis of said second bore and having inner adjacent surfaces tapering to diverge upwardly; a wedge in said second bore having tapered surfaces complementary to said: inner adjacent surfaces and said wedge extending upwardly out of said second bore and beyond the end of said rod, whereby as said rod'is pushed into said first bore the wedge will bottom on said blind end and be forced downwardly with respect to said slips thereby expanding the slips laterally outwardly to embed them in the walls of the first bore so that a downward pull on said rod will cause said slips to wedge deeper into the tapers of said slots and expand said upper end.

11. In'a device as set forth in claim 10, said slips each having an outer bore-engaging surface having striations thereon to tightly grip the walls of said first bore, and the lower end of said slips each being undercut to leave tooth-like projections to prevent shifting of said slips axially of said first bore. 1 12. In a device as set forthin claim 10, said first bore being deeper than the length of said rod, and said rod having a screw hole in its lower end; a bearing plate having a hole therethrough, and a screw adapted to transfix said holes, whereby when said rod is inserted in said first bore with its lower end above the roof of the mine and said screw is tightened, the rod will be forcibly moved downwardlyin said first bore to wedge said slips.

13. An anchor for securing a rod in acomplementary bore having a blind end, comprising a rod bifurcated at its inner end by a slot extending axially thereinto, the slot being tapered to converge toward its open end; a pair of complementarily tapered slips in said slot, the slips being spaced apart and having inner adjacent surfaces tapered to diverge toward the open end of the slot; a wedge between said slips having a taper complementary to that of said inner adjacent surfaces; and an elongated trip bar fixed to said wedge and extending outwardly through the open end of the slot beyond the end of the rod, whereby as said rod is pushed into said bore the trip bar will bottom on said blind end and force said wedge between said slips thereby expanding the latter outwardly to embed them in the walls of said bore so that any subsequent outward motion of said rod with respect to said bore will cause said slips to wedge deeper into the taper of said slot and expand said bifurcated irmer end.

14. In a device as set forth in claim 13, said slips each having an outer bore-engaging surface having striations thereon to tightly grip the walls of said bore, and the ends of said slips opposite from the open end of the slot being undercut to leave tooth-like projections to prevent shifting of said slips axially of said bore.

15. An anchor for securing a rod in a complementary bore having a blind end, comprising a rod bifurcated at its inner end by a slot extending axially thereinto, the slot being tapered to converge toward its open end; a pair of complementarily tapered slips in said slot, the slips being spaced apart and having inner adjacent attain surfaces tapered to diverge toward the open 'end 'of thGzSIOt; ;a wedge-between said slips having a tap'er complementary to that of said innerad- Fjacent surfaces and said wedge ex-tending outwardly through the open end-of .the slot beyond theend: of the rrod, whereby as: said rod: is pushed into said bore the wedge will bottom on said :blindendand be forced between said slips there- :by expanding the latter outwardly to embed=them in the walls of said bore so that any subsequent outward motion of said-rod with. respect to said. bore will cause saidslips .to wedge deeper into ithe taper of :said-slot-and-expand said bifurcated inner-end.

16. In a device Iasset forth in claim 15, said slips each having an outer bore-engaging suriaceha-vin'g striations thereon to tightly grip the walls of said bore, and :the ends of saidslips opposite from the open end of the slot being undercut to leave tooth-like projections-to prevent shifting of said slipszaxially of said bore.

17. An anchor for securing a rod in a complementary bore having a blindlend, comprising a rod having-a slot extending axially into its .inner :end, the slot being tapered to converge toward its open end; ap'air-of complementarily taperedslips in said, slot, the slips having inner adjacent surfaces tapered to diverge toward the open end of the slot; a wedge between said slips having a taper complementary to that of said inneradjacent surfaces-and said wedge extending outwardly through the open :end'of the slot be- .yond the end of the rod, whereby as said rod is pushedinto said bore the wedge will bottom on said blind end and be forced between said slips thereby expanding the-latter outwardly to'embed them in the wallsof saidbore so that any subsequent outward-motion ofsaid rod with respect to said bore will cause said slips to wedge deeper into-the taper'of said slot:and expand the inner end of the rod.

18. In a device as-set-forthin-claim-ii, said :slips *each'having an outerboreibore-engaglng surface havin striations thereon to tightly-grip the walls of said bore, and theends of said slips opposite :from the open end of the slot being undercut to leave tooth-like projections to prevent shifting of said slips axially of said bore.

19. An anchor for securing a rod in a complementary bore having a blind end, comprisinga rod having a concentric bore in its inner end and slots through its inner end communicating with said second bore, the-slots being tapered to converge toward said inner end; a complementarily tapered slip in each slot, the slipsbelng spaced from the axis of said second bore and having inner adjacent surfaces tapered to diverge toward the'inner end of the rodpa wedge insaid second bore having tapered surfacescom- .plementary to said inner adjacent surfaces and slips each having an'outer bore-engaging surface having striations thereon to tightly grip the walls of said firstbore, and the ends of said slips opposite from the open ends of the slots being undercut-to leavetooth-vlike projections to prevent shifting of said slips axially of-said first bore.

SAMUEL J. CROCKETT.

No references cited. 

